How to: 2000 TC HIF6 Carb Conversion


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The 2 inch HS8's. We had fun together, but sometimes it's just time to move on...

As some of you may know, I have recently converted my 2000 TC to run on the twin SU HIF6 carburettor setup of the later 2200 TC models. I'm very pleased with the new setup, and am currently enjoying the increased torque and economy as anticipated.
For anybody considering the conversion, I thought it might be worthwhile to put all of the salient points of the conversion into one post, as I had to glean a lot of information from various places before starting, and even then had to experiment somewhat to get the setup how I wanted it.
I don't wish to detract from Demetris' excellent post last year :) - which in all honesty was the inspiration for my own conversion :D - I just want to highlight the things I had to find out along the way.

My car is a RHD UK spec Series II 2000 TC, and originally had the stock twin SU HS8 carburettors as fitted 1970-73 (engraved flat-topped float chambers, and crankcase emission pipes).

-SU HIF6 carbs from 2200 TC. Complete assembly including all mounting brackets, tie plates and balance bars. No need for manifold or exhaust heat-shield.
-Throttle linkage rod-to-cable 'see-saw' adapter.
-Length of rubber fuel hose.
-2200 TC throttle cable.
-SC or universal choke cable, and grub screw cable grip fitting from HS8 choke lever.
-Air filter solution.

The original manifold can be retained, and need not be detached from the car during the conversion. A longer non-return brake servo valve with separate banjo fitting to operate the HIF6's air filter box internal valves can be obtained if desired.

The usual rules apply to servicing the carbs, so I won't go into it. However, as the float chambers are inverted and inaccessible when the carbs are in position, it is essential to check the condition (or replace) the O-ring seal on the float chamber lid, and in the brass choke 'tap' to prevent leaks.
To set the float level, remove the cover, invert the carb and place a ruler across the top, passing through the centre. The middle of the float's curved side (half way along its length), should sit 1mm below (+/- 0.5mm) the ruler's edge. Bend the brass tab against the valve to adjust. Check the bi-metallic jet adjusting bracket correctly engages the jet and lowers it when the screw is turned.

The needles should be biased (tip of needle) towards the throttle discs (as opposed to the air filter). The stock 2200 needles (BBX) perform reasonably well, but I'm sure careful experimentation could yield better results.

Along with the manifold, the exhaust heat shield, and flexible-mounting adapter plate for the rear carburettor only can all be retained from the HS8 setup. You will need a second adapter plate for the front caburettor, as the cast-in throttle shaft bracket on the HS8 setup fouls the HIF6 carb body.
The flexibly-mounted tie-bar and spring, the cable mounting point, and the carburettor link plate must all be changed for the 2200TC setup.

I found the easiest way to fit the carbs was:
-Remove the adapter plates from the manifold by extracting the two 1/2 AF bolts (top and bottom) and levering them free. Check the condition of the rubber O-rings and smear them with some silicon grease and ease them back into the grooves in the manifold.
-Fit the flexibly-mounted tie-bar and spring.
-Bolt each carb to its adapter plate (making sure the brackets for the exhaust heat shield are on the right sides). Place the throttle and choke balance bars loosely in place between the two carbs and offer them both up to the manifold as one unit.
-Push them squarely home and then refit the 1/2 bolts. If they don't go cleanly in, the bolts can be used to pull them in. A good waggle should get them in - be persistent, the rubber O-rings have to be squeezed round the adapter plates' shoulders.
-Fit the link-plate across the front of the carbs.
-Tension the spring with the adjusting nut until the gap between the manifold and adapter plates are equal on all sides.
-Bolt the heat shield on underneath with the 7/16 AF bolts.

The standard 2000 TC fuel pipe (from the pump to the carbs) is too short to reach the HIF6 setup. It could be extended (ideally with an in-line filter), but needs a 90 degree bend at the end which causes the hard plastic to kink. So either mate some rubber onto it, or for the easy life just get a pipe off a 2200 SC or TC (they both have the bend in the end, and are long enough to reach).
You will also need a 7" length of rubber fuel pipe (int diam 6mm) to supply fuel to the rear carb from the front, and some jubilees to fit.

Can be retained without compromise as far as the double-ended ball-joint rod at the steering idler bracket.
The rod-to-cable 'see-saw' throttle adapter from the 2200 TC setup is bolted onto the steering idler bracket in place of the throttle shaft retaining bracket of the 2000 TC setup with 9/16 AF bolts. Elliptical slotted holes allow a limited amount of adjustment - mounting the adapter at the top of this travel will give the greatest range of adjustment elsewhere.
If the ball-joint is missing on the see-saw adapter, one can be obtained separately as part no 14 on page 22N, 24N & 26N of the Rover 2000 workshop manual. It just bolts in place.
The throttle cable is a special part with adjustment threads at either end and bespoke fittings. It is not possible to make one up from a universal cable. Wadhams sell remanufactured items for under £30 after VAT and delivery.

The advantage of the throttle cable is that it allows all of the 'slack' to be taken out of the linkage for a much more responsive pedal action. However, this sets the pedal very high and at an uncomfortable angle. The solution is to the screw-in the throttle pedal stop bolt in the footwell until the pedal is at a comfortable position. Then adjust the cable securing nuts at either end of the cable until it has been extended sufficiently to allow the throttles to close. If this is not possible (ie, the cable is too short), move the cable securing nuts to the inner ends of their threads, tighten them, and then unscrew the pedal stop bolt until the throttles are just closing (idler screws touching the carb bodies), and then unscrew a further 1/4 turn. Over the first 100 miles or so, the cable will stretch significantly, and this slack can be taken back up at the pedal if desired.

Unlike the HS8 setup, HIF6s have a choke balance bar, so only one cable is needed to operate both carbs (a great improvement!). A universal choke cable fits easily, but if you want to keep the original choke knob/indicator light arrangement you need to get an SC choke cable. One of the grub screw fittings that holds the cable to the choke mech on the HS8 setup is needed to secure the new cable to the balance bar. A 9/16 AF open jaw spanner releases the choke knob from behind the speaker grille. A mirror helps!

Fire up, set, balance, and tune!

Despite my belligerent intentions, it is definitely NOT possible to fit the original 2000 TC air filter box to the later setup. The original box requires the round cast aluminium adapter plates to fit, and as the air intake holes on these plates are bigger than those on the front of the HIF6 carburettors, unnecessary air turbulence would be generated. That, and the plates would need to be extensively modified to fit.
The only options are to fit the correct 2200 TC air box (which has an automatic warm-air valve, requiring the banjo fitting on the brake-servo non-return valve), or chrome pancake filters. I've made up some pancake type ones for the time being (as I can't get hold of the proper filter box), but can confirm that the induction roar is not intrusive, and only audible at full-throttle at low road speeds.

Original HS8 carbs before conversion.

Old and New. HIF6 on the left is a considerably more compact carb.

Manifold and heatshield need not be removed. Front carburettor adaptor plate must be changed for one without the throttle bar. New (shorter) tie-bar and spring was fitted at this point.

Rod-to-cable 'see-saw' adapter bolted to the steering idler bracket. Cable length adjustment thread visible at top.

Complete HIF6 setup in place. Temporary air filters are homemade from aluminium sheet, steel wire, glue and stock filters. Beady-eyed ones will notice that the crankcase ventilation inlets on the carbs have been connected together with a balance pipe. I chose to remove the crankcase ventilation pipes and route them away beneath the car.

Hopefully that covers just about everything.



Active Member
Thanks for the write up with photos. I was wondering if this conversion will work with any 1¾" carbs? For example, your engine had HS8 carbs as standard so would it have been a straight swap, ie using the standard throttle linkage, to fit HS6 carbs instead? HS6 carbs from V8 engines are pretty common and readily available cheaply on eBay.


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testrider said:
HS6 carbs from V8 engines are pretty common and readily available cheaply on eBay.
The float chamber on a V8 fitted HS6 is at a different angle from that fitted to a 4 pot due to the angle the carb is mounted to the V8 manifold. I know the float chamber is removable and is keyed, but can the orientation be altered to suit 4 pot applications?

:oops: quick edit as I almost forgot ......excellent write up there Michael :D



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testrider said:
I was wondering if this conversion will work with any 1¾" carbs?
I thought about this too, but I don't think I'd fancy it. If you ground away the key on the float chamber mount it might just be possible (and the mounting PCD is the same) but the hard bit would be making everything else fit around it. As you can see from the pics, the sprung tie bar is shorter for the smaller carbs, so straight away you're into modification-territory. After that, there's the issue of tying the carbs together with a suitable front plate. I think that should be relatively easy enough, but it's the linkages that would put me off. I'm not overly familiar with the V8 carb setup, but if you place them side-by-side do the throttle shaft holes face each other and line up? If they do you might be able to fit something between them (ideally the old balance shaft) and attach a cable to that some way, or give it a go with a twin-cable setup...??
There's plenty of space so I'm sure you could manage something, but it would be a lot of faff, and I'm not sure it would be worth it. Part of the reason I did this thread was to show how easy the conversion is to earlier models, as well as to list the parts required - something I had to work out for myself as I went along.
That said, if you could make it work I'd be very interested to see it. I love the cleverness of the HIF-type carb, but would feel a lot more at ease with the simplicity of the HS-type.



Active Member
Beady-eyed ones will notice that the crankcase ventilation inlets on the carbs have been connected together with a balance pipe. I chose to remove the crankcase ventilation pipes and route them away beneath the car.
Just read over this excellent post and only one thing got me wondering - why did you choose not to connect the crankcase ventilation to the carbs?


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JVY said:
Just read over this excellent post and only one thing got me wondering - why did you choose not to connect the crankcase ventilation to the carbs?
Because they aren't really necessary any more, and it's just adding unnecessary variance to an area that needs to be as precise and unvarying as possible: carburetion.
Crankcase ventilation was just a way minimize the amount of 'potentially harmful' gasses escaping from the engine in order to make the engine comply with some arbitrary figure in a now long outdated set of environmental regulations. Pre 1971 P6's didn't have the system at all, and I figured that since the carbon monoxide escaping from my non-catalysed exhaust far outweighs the quantities of 'potentially harmful' blow-by gasses that might find their way into the crankcase, there's no reason why they need to be burned with combustion any more. As long as you don't breathe them, you're alright, so I routed some pipes away beneath the engine to either side of the bell-housing where get wafted away without issue. Very occasionally, I will get a small drip come out of one, but nothing more than that.

The real advantage is that they no longer spew oily, filmy, horrible dirty air straight into the carb. This can cover the throttle disc, the back of the piston, presumably coat the inlet ports to upset swirl, and crucially introduces a variance in the atomising of fuel. When the engine is at higher speeds, there is greater crankcase ventilation, and therefore more 'bad air' being forced through the pipes. When faced with the choice of pressurized air from a tube, or atmospheric pressure air on the other side of a carburettor piston, the carb will suck from the tube every time. But because this varies so much with engine speed and condition, and because the carbs are connected to different crank case tubes, you're chasing a white rabbit trying to get the damn things in tune. Blocking up the pipe inlets (as I have done since this picture with a silicon sealant and steel 'bung') means that all of the induction air comes over the carb bridge. It runs a little richer now, so I'm thinking about a different needle choice, but the performance is much quicker and much, much smoother to idle.

I don't think it's wise to do this on a V8, but others will be able to give a more detailed run down on exactly why.



Active Member
Thanks for such a full reply Michael. All your reasoning sounds sensible (at least to a novice like me). What you say about maybe using dfferent needles sounds interesting as I wondered if Rover had selected the standard 2200TC BBX needles to take account of the crankcase bening vented to the carbs?

When you say you have bunged up the inlets, do you mean that you have removed the balancing pipe between carbs? Did this make a further improvement? Also, I wondered if you had noticed any change in MPG since you did the work?


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JVY said:
I wondered if Rover had selected the standard 2200TC BBX needles to take account of the crankcase bening vented to the carbs?
Oh undoubtedly in my opinion. They're quite rich at the top end (and especially on my 2000 engine!) now that the pipes have gone. I presume this was to counter the additional air from the pipes at high engine speeds and wider throttle openings (ie, motorway cruise). Mine was a tad thirstier for a while, but I leaned them out a touch to find a compromise until I work out a better needle.
I only removed the 'balance pipe' to neaten everything up under the bonnet. The manifold acts as the balance, as both carbs act on the brake servo hose. My extra hose was just a temporary fix until I had worked out how to permanently seal the inlets - the idea being that if they both drew on each other, there was no chance of air getting in.



Staff member
When i run a generic 2litre ohc engine through the su carb program it suggests BDQ which is leaner accross most of the range than BBX.



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Hmmm... Thanks Rich, Might be worth thinking about that.

It is certainly super rich (like 17mpg) at 70+ mph, and the plugs are really fouled around the edges (though not the electrode, as I deliberately have the slightly hotter N9Y plugs). I once got a tiny touch of running on - less than 2 secs or so - after a long motorway run, so it's definitely too rich at the top end. I don't do the M6 anymore!!

The middle range is also slightly richer than ideal, as sustained extra-urban 50 mph driving leaves a lovely speckly brown deposit on the electrode, but minor dark grey fouling round the rim, so that BDQ sounds a lot more appropriate to intentions. I used colourtune, but there's no way to put the engine under load, so I only use it as a guide to setting them up.

I may pick your software's brain sometime soon if that's okay? Got to sort out the induction first though. Some ram pipes, a plenum and a big juicy filter to go on. Lovely!



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I chose to retain the standard engine breathing system after the HIF conversion in my 2000 TC. The reason is that with negative pressure within the crankcase, you reduse the possibility of various oil leaks. Also since my engine continues to be in excellent health, there is not much, if any, piston blowby to drawn in the carbs and upset the mixture.
I still run the standard 2200 TC needles, with the standard air filter and case. I find that the car runs fine like this, economy is excellent as you can see in my fuelly gauge below, and the carbs did not require any tuning since i fitted them. I guess that the replacement free-flow exhaust back box helps to even the mixture strength requirements, and i am still thinking at a K&N replacement filter element too.


Staff member
Interestingly it suggests the 2.2 setting that bbx is too rich too, so could be this engine has characteristics not mapped by the program!

The only true way to gauge it is lambda sensors on the exhaust or a rolling road i guess.



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The Burlen site is right. BBX needles are the recommended needles for the 2200 TC, and that's definitely what I have in mine (brand new with new jets to circumvent any issues associated with wear). Interesting that they show as too rich. Although this would concur with the original leaded fuel wouldn't it? Unleaded needs to be a tad richer doesn't it? Either that or it points to just how much crankcase gasses come through.

Demetris, the negative crankcase pressure argument is a good one, and I never thought of it that way before. At speed, the gasses will be drawn out of the pipe underneath my car, but not with anywhere near the force that the manifold vacuum could draw them. Interesting.....



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I have used that needle selection program in the past too, and although for popular engines that their tuning possibilities have been discussed and tried to death (A, B series, RV8) in most cases it can give you a decent ballpark figure, the suggestions for Rover's OHC 4cyl should be completely irrelevant. I cannot imagine that the Rover OHC 4, the O series, an enlarged B series and the 2 litre Pinto for example have the same carburation needs. Instead for searching for needles in a haystack ( :LOL: ) i think it's better to stick to the factory selection for the 2200 and try to improve the engine breathing to counterbalance the smaller displacement.
Regarding crankcase ventilation, i actually think that the negative pressure promotes free revving too, more so than an atmosphere vented system, especially in unworn engines with negligible blowby.


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I think you're right Rich. Weaker needles across the range do sound a lot more appropriate to my intentions (crankcase pipes removed, etc) than the BBX's, but Demetris is right pointing out what 'generic 2 litre 4 cyl' actually means. I think combustion chamber shape, compression ratio and volumetric flow are going to be variables equally as significant as the displacement itself. :(
Right, time to start thinking about scraping together some pennies and doing something I don't do very often... taking the car to a man with a big tool!